Wolf Fact
Facts The wolf also known as the gray wolf, timber wolf, western wolf, and its other subspecies is a canine native to the wilderness and remote areas of Eurasia and North America. It is the largest extant member of its family, with males averaging 43–45 kg and females 36–38.5 kg –85. Like the red wolf, it is distinguished from other Canes species by its larger size and less pointed features, particularly on the ears and muzzle. Its winter fur is long and bushy and predominantly a mottled gray in color, although nearly pure white, red, and brown to black also occur. Mammal Species of the World a standard reference work in zoology, recognizes 38 subspecies of lupus. The gray wolf is the second most specialized member of the genus Canes, after the Ethiopian wolf, as demonstrated by its morphological adaptations to hunting large prey, its more gregarious nature, and its highly advanced expressive behavior. It is nonetheless closely related enough to smaller Canes species, such as the eastern wolf, coyote, and golden jackal to produce fertile hybrids. It is the only species of Canes to have a range encompassing both the Old and New Worlds, and originated in Eurasia during the Pleistocene, colonizing North America on at least three separate occasions during the Rancholabrean. It is a social animal, travelling in nuclear families consisting of a mated pair, accompanied by the pair's adult offspring. The gray wolf is typically an apex predator throughout its range, with only humans and tigers posing a serious threat to it. It feeds primarily on large ungulates, though it also eats smaller animals, livestock, carrion, and garbage. A seven year-old wolf is considered to be relatively old, and the maximum lifespan is about 16 years. The gray wolf is one of the world's best-known and most-researched animals, with probably more books written about it than any other wildlife species. It has a long history of association with humans, having been despised and hunted in most pastoral communities because of its attacks on livestock, while conversely being respected in some agrarian and hunter-gatherer societies. Although the fear of wolves is pervasive in many human societies, the majority of recorded attacks on people have been attributed to animals suffering from rabies. Non-rabid wolves have attacked and killed people, mainly children, but this is rare, as wolves are relatively few, live away from people, and have developed a fear of humans from hunters and shepherds. The English 'wolf' stems from the Old English wulf, which is itself thought to be derived from the Proto-Germanic *wulfaz. The Latin lupus is a Sabine loanword. Both derive from the Proto-Indo-European root *wlqwos or *lukwos. Taxonomy and evolution Taxonomy Main article: Subspecies of Canis lupus The species Canis lupus was first recorded by Carl Linnaeus in his publication Systema Naturae in 1758, with the Latin classification translating into the English words "dog wolf". The thirty-seven subspecies of Canis lupus are listed under the designated common name of "wolf" in Mammal Species of the World third edition that was published in 2005. The nominate subspecies is the Eurasian wolf (Canis lupus lupus), also known as the common wolf. The subspecies includes the domestic dog, dingo, eastern wolf and red wolf, but lists C. l. italicus and C. l. communis as synonyms of C. l. lupus. However, the classification of several as either species or subspecies has recently been challenged. Origin Main article: Evolution of the wolf Artist's impression of a Beringian wolf The evolution of the wolf occurred over a geologic time scale of at least 300 thousand years. The gray wolf Canis lupus is a highly adaptable species that is able to exist in a range of environments and which possesses a wide distribution across the Holarctic. Studies of modern gray wolves have identified distinct sub-populations that live in close proximity to each other. This variation in sub-populations is closely linked to differences in habitat - precipitation, temperature, vegetation, and prey specialization - which affect cranio-dental plasticity. The archaeological and paleontological records show gray wolf continuous presence for at least the last 300,000 years. This continuous presence contrasts with genomic analyses, which suggest that all modern wolves and dogs descend from a common ancestral wolf population that existed as recently as 20,000 years ago. These analyses indicate a population bottleneck, followed by a rapid radiation from an ancestral population at a time during, or just after, the Last Glacial Maximum. However, the geographic origin of this radiation is not known. Population structure In 2013, a genetic study found that the wolf population in Europe was divided along a north-south axis and formed five major clusters. Three clusters were identified occupying southern and central Europe in Italy, the Dinaric-Balkans, the Carpathians. Another two clusters were identified occupying north-central Europe and the Ukrainian steppe. The Italian wolf consisted of an isolated population with low genetic diversity. Wolves from Croatia, Bulgaria, and Greece formed the Dinaric-Balkans cluster. Wolves from Finland, Latvia, Belarus, Poland and Russia formed the north-central Europe cluster, with wolves from the Carpathians cluster coming from a mixture of wolves from the north-central cluster and the Dinaric-Balkans cluster. The wolves from the Carpathians were more similar to the wolves from the Pontic-Caspian Steppe than they were to wolves from north-central Europe. These clusters may have been the result of expansion from glacial refugia, an adaptation to local environments, and landscape fragmentation and the killing of wolves in some areas by humans. In 2016, two genetic studies of North American gray wolves found that they formed six ecotypes – genetically and ecologically distinct populations separated from other populations by their different type of habitat. These six wolf ecotypes were named West Forest, Boreal Forest, Arctic, High Arctic, Baffin, and British Columbia. The studies found that precipitation and mean diurnal temperature range were the most influential variables. These findings were in accord with previous studies that precipitation influenced morphology and that vegetation and habitat type influenced wolf differences.38 The local adaptation of a wolf ecotype most likely reflects a wolf's preference to remain in the type of habitat that it was born into. Hybridization with other Canis Main article: Canid hybrid F1 wolf-dog hybrids from Wildlife Park Kadzidlowo, Poland. The first is the product of a male wolf and a female spaniel, while the latter comes from a female wolf and a male West Siberian Laika It was once thought that dogs and gray wolves did not voluntarily interbreed in the wild, though they can produce fertile wolf-dog offspring. In 2010, a study of 74 Italian wolf male lineages found that 5 of them originated from dog ancestry, indicating that female wolves will breed with stray male dogs in the wild. In North America, black colored wolves acquired their coloration from wolf-dog hybridization, which occurred 10,000–15,000 years ago. Like pure wolves, hybrids breed once annually, though their mating season occurs three months earlier, with pups mostly being born in the winter period, thus lessening their chances of survival. However, one genetic study undertaken in the Caucasus Mountains showed that as many as 10% of dogs in the area, including livestock guardian dogs, are first generation hybrids. The captive breeding of wolf-dog hybrids has proliferated in the United States, where there is an estimated population of 300,000. The gray wolf has interbred extensively with the eastern wolf producing a hybrid population termed Great Lakes boreal wolves. Unlike the red and eastern wolf, the gray wolf does not readily interbreed with coyotes. Nevertheless, coyote genetic markers have been found in some wild isolated gray wolf populations in the southern United States. Gray wolf Y-chromosomes have also been found in Texan coyote haplotypes. In tests performed on a Texan canid of ambiguous species, mtDNA analysis showed that it was a coyote, though subsequent tests revealed that it was a coyote–gray wolf hybrid sired by a male Mexican gray wolf. In 2013, a captive breeding experiment in Utah between gray wolves and western coyotes produced six hybrids through artificial insemination, making this the first hybridization case between pure coyotes and northwestern gray wolves. At six months of age, the hybrids were closely monitored and were shown to display both physical and behavioral characteristics from both species. Although hybridization between wolves and golden jackals has never been observed, evidence of such occurrences was discovered through mtDNA analysis on jackals in Bulgaria. Although there is no genetic evidence of gray wolf-jackal hybridization in the Caucasus Mountains, there have been cases where otherwise genetically pure golden jackals have displayed remarkably gray wolf-like phenotypes, to the point of being mistaken for wolves by trained biologists. Physical description Anatomy and dimensions Differences between gray wolf and coyote Gray wolf skeleton Wolf mandible diagram showing the names and positions of the teeth. The gray wolf is the largest extant member of the Canidae, excepting certain large breeds of domestic dog. Gray wolf weight and size can vary greatly worldwide, tending to increase proportionally with latitude as predicted by Bergmann's Rule, with the large wolves of Alaska and Canada sometimes weighing 3–6 times more than their Middle Eastern and South Asian cousins. On average, adult wolves measure 105–160 cm (41–63 in) in length and 80–85 cm (31–33 in) in shoulder height. The tail measures 29–50 cm (11–20 in) in length. The ears are 90–110 mm (3.5–4.3 in) in height, and the hind feet are 220–250 mm (8.7–9.8 in). The mean body mass of the extant gray wolf is 40 kg (88 lb), with the smallest specimen recorded at 12 kg (26 lb) and the largest at 79.4 kg (175 lb). Gray wolf weight varies geographically; on average, European wolves may weigh 38.5 kg (85 lb), North American wolves 36 kg (79 lb) and Indian and Arabian wolves 25 kg (55 lb). Females in any given wolf population typically weigh 5–10 lb (2.3–4.5 kg) less than males. Wolves weighing over 54 kg (119 lb) are uncommon, though exceptionally large individuals have been recorded in Alaska, Canada, and the forests of western Russia. The heaviest recorded gray wolf in North America was killed on 70 Mile River in east-central Alaska on July 12, 1939 and weighed 79.4 kg (175 lb). Compared to its closest wild cousins (the coyote and golden jackal), the gray wolf is larger and heavier, with a broader snout, shorter ears, a shorter torso and longer tail. It is a slender, powerfully built animal with a large, deeply descending ribcage, a sloping back and a heavily muscled neck. The wolf's legs are moderately longer than those of other canids, which enables the animal to move swiftly, and allows it to overcome the deep snow that covers most of its geographical range. The ears are relatively small and triangular. Females tend to have narrower muzzles and foreheads, thinner necks, slightly shorter legs and less massive shoulders than males. The gray wolf usually carries its head at the same level as the back, raising it only when alert. It usually travels at a loping pace, placing its paws one directly in front of the other. This gait can be maintained for hours at a rate of 8–9 km/h (5.0–5.6 mph), and allows the wolf to cover great distances. On bare paths, a wolf can quickly achieve speeds of 50–60 km/h (31–37 mph). The gray wolf has a running gait of 55–70 km/h (34–43 mph), can leap 5 m (16 ft) horizontally in a single bound, and can maintain rapid pursuit for at least 20 minutes. Generally, wolves have a high heart weight of 0.93%-1.07% total body mass compared to the average mammal at 0.59% total body mass. Wolves have a decreased heart rate suggesting cardiac enlargement and hypertrophy. Tibetan gray wolves, which occupy territories up to 3,000 above sea level, have evolved hearts that withstand the low oxygen levels. Specifically, these wolves have a strong selection for RYR2, a gene that initiates cardiac excitation. Skull and dentition The gray wolf's head is large and heavy, with a wide forehead, strong jaws and a long, blunt muzzle. The skull averages 230–280 mm (9.1–11.0 in) in length, and 130–150 mm (5.1–5.9 in) wide. The teeth are heavy and large, being better suited to crushing bone than those of other extant canids, though not as specialised as those found in hyenas. Its molars have a flat chewing surface, but not to the same extent as the coyote, whose diet contains more vegetable matter. The gray wolf's jaws can exert a crushing pressure of perhaps 10,340 kPa (1,500 psi) compared to 5,200 kPa (750 psi) for a German shepherd. This force is sufficient to break open most bones. A study of the estimated bite force at the canine teeth of a large sample of living and fossil mammalian predators when adjusted for the body mass found that for placental mammals, the bite force at the canines (in Newtons/kilogram of body weight) was greatest in the extinct dire wolf (163), then followed among the extant canids by the four hypercarnivores that often prey on animals larger than themselves: the African hunting dog (142), the gray wolf (136), the dhole (112), and the dingo (108). A similar trend was found with the carnassial tooth bite force, but with the extinct dire wolf and gray wolf both measuring (141), then followed by the African hunting dog (136), the dhole (114), and the dingo (113). See also: Dog anatomy Fur Black and white-furred gray wolves The gray wolf has very dense and fluffy winter fur, with short underfur and long, coarse guard hairs. Most of the underfur and some of the guard hairs are shed in the spring and grow back in the autumn period. The longest hairs occur on the back, particularly on the front quarters and neck. Especially long hairs are on the shoulders, and almost form a crest on the upper part of the neck. The hairs on the cheeks are elongated and form tufts. The ears are covered in short hairs, which strongly project from the fur. Short, elastic and closely adjacent hairs are present on the limbs from the elbows down to the calcaneal tendons. The winter fur is highly resistant to cold; wolves in northern climates can rest comfortably in open areas at −40° by placing their muzzles between the rear legs and covering their faces with their tail. Wolf fur provides better insulation than dog fur, and does not collect ice when warm breath is condensed against it. In warm climates, the fur is coarser and scarcer than in northern wolves. Female wolves tend to have smoother furred limbs than males, and generally develop the smoothest overall coats as they age. Older wolves generally have more white hairs in the tip of the tail, along the nose and on the forehead. The winter fur is retained longest in lactating females, though with some hair loss around their nipples. Hair length on the middle of the back is 60–70 mm (2.4–2.8 in). Hair length of the guard hairs on the shoulders generally does not exceed 90 mm (3.5 in), but can reach 110–130 mm (4.3–5.1 in). Coat color ranges from almost pure white through various shades of blond, cream, and ochre to grays, browns, and blacks, with variation in fur color tending to increase in higher latitudes. Differences in coat color between sexes are largely absent, though females may have redder tones. Black-colored wolves in North America inherited the Kb allele responsible for melanism from past interbreeding with dogs, while the mutation was found to be naturally occurring in wolves from Iran. Black specimens are more common in North America than in Eurasia, with about half the wolves in Yellowstone National Park being black. Behavior See also: Dog behavior Social and territorial behaviors Gray wolf pack The gray wolf is a social animal, whose basic social unit consists of a mated pair, accompanied by the pair's adult offspring. The average pack consists of a family of 5–11 animals (1–2 adults, 3–6 juveniles and 1–3 yearlings), or sometimes two or three such families, with exceptionally large packs consisting of up to 42 wolves being known. In ideal conditions, the mated pair produces pups every year, with such offspring typically staying in the pack for 10–54 months before dispersing. Triggers for dispersal include the onset of sexual maturity and competition within the pack for food. The distance travelled by dispersing wolves varies widely; some stay in the vicinity of the parental group, while other individuals may travel great distances of 206 km (128 mi), 390 km (240 mi), and 670 km (420 mi) from their natal packs. A new pack is usually founded by an unrelated dispersing male and female, travelling together in search of an area devoid of other hostile packs. Wolf packs rarely adopt other wolves into their fold, and typically kill them. In the rare cases where other wolves are adopted, the adoptee is almost invariably an immature animal (1–3 years of age) unlikely to compete for breeding rights with the mated pair. In some cases, a lone wolf is adopted into a pack to replace a deceased breeder. During times of ungulate abundance (migration, calving etc.), different wolf packs may temporarily join forces. Studies of wolves' cortisol levels show that they rise significantly when a pack member dies, indicating the presence of stress. Wolves are highly territorial animals, and generally establish territories far larger than they require to survive in order to assure a steady supply of prey. Territory size depends largely on the amount of prey available and the age of the pack's pups, tending to increase in size in areas with low prey populations or when the pups reach the age of 6 months, thus having the same nutritional needs as adults. Wolf packs travel constantly in search of prey, covering roughly 9% of their territory per day (average 25 km/d (16 mi/d)). The core of their territory is on average 35 km2 (14 sq mi), in which they spend 50% of their time. Prey density tends to be much higher in the territory's surrounding areas, though wolves tend to avoid hunting in the fringes of their range unless desperate, because of the possibility of fatal encounters with neighboring packs. The smallest territory on record was held by a pack of six wolves in northeastern Minnesota, which occupied an estimated 33 km2 (13 sq mi), while the largest was held by an Alaskan pack of ten wolves encompassing a 6,272 km2 (2,422 sq mi) area. Wolf packs are typically settled, and usually only leave their accustomed ranges during severe food shortages. Wolves defend their territories from other packs through a combination of scent marking, direct attacks and howling (see Communication). Scent marking is used for territorial advertisement, and involves urination, defecation and ground scratching. Scent marks are generally left every 240 m (260 yd) throughout the territory on regular travelways and junctions. Such markers can last for 2–3 weeks, and are typically placed near rocks, boulders, trees, or the skeletons of large animals. Territorial fights are among the principal causes of wolf mortality, with one study concluding that 14–65% of wolf deaths in Minnesota and the Denali National Park and Preserve were due to predation by other wolves. © The gray wolf is the largest extant member of the Canidae, excepting certain large breeds of domestic dog. Gray wolf weight and size can vary greatly worldwide, tending to increase proportionally with latitude as predicted by Bergmann's Rule, with the large wolves of Alaska and Canada sometimes weighing 3–6 times more than their Middle Eastern and South Asian cousins. On average, adult wolves measure 105–160 cm (41–63 in) in length and 80–85 cm (31–33 in) in shoulder height. The tail measures 29–50 cm (11–20 in) in length. The ears are 90–110 mm (3.5–4.3 in) in height, and the hind feet are 220–250 mm (8.7–9.8 in). The mean body mass of the extant gray wolf is 40 kg (88 lb), with the smallest specimen recorded at 12 kg (26 lb) and the largest at 79.4 kg (175 lb). Gray wolf weight varies geographically; on average, European wolves may weigh 38.5 kg (85 lb), North American wolves 36 kg (79 lb) and Indian and Arabian wolves 25 kg (55 lb). Females in any given wolf population typically weigh 5–10 lb (2.3–4.5 kg) less than males. Wolves weighing over 54 kg (119 lb) are uncommon, though exceptionally large individuals have been recorded in Alaska, Canada, and the forests of western Russia.10 The heaviest recorded gray wolf in North America was killed on 70 Mile River in east-central Alaska on July 12, 1939 and weighed 79.4 kg (175 lb). Compared to its closest wild cousins (the coyote and golden jackal), the gray wolf is larger and heavier, with a broader snout, shorter ears, a shorter torso and longer tail. It is a slender, powerfully built animal with a large, deeply descending ribcage, a sloping back and a heavily muscled neck. The wolf's legs are moderately longer than those of other canids, which enables the animal to move swiftly, and allows it to overcome the deep snow that covers most of its geographical range. The ears are relatively small and triangular. Females tend to have narrower muzzles and foreheads, thinner necks, slightly shorter legs and less massive shoulders than males. The gray wolf usually carries its head at the same level as the back, raising it only when alert. It usually travels at a loping pace, placing its paws one directly in front of the other. This gait can be maintained for hours at a rate of 8–9 km/h (5.0–5.6 mph), and allows the wolf to cover great distances. On bare paths, a wolf can quickly achieve speeds of 50–60 km/h (31–37 mph). The gray wolf has a running gait of 55–70 km/h (34–43 mph), can leap 5 m (16 ft) horizontally in a single bound, and can maintain rapid pursuit for at least 20 minutes. Generally, wolves have a high heart weight of 0.93%-1.07% total body mass compared to the average mammal at 0.59% total body mass. Wolves have a decreased heart rate suggesting cardiac enlargement and hypertrophy. Tibetan gray wolves, which occupy territories up to 3,000 above sea level, have evolved hearts that withstand the low oxygen levels. Specifically, these wolves have a strong selection for RYR2, a gene that initiates cardiac excitation. The gray wolf's expressive behavior is more complex than that of the coyote and golden jackal, as necessitated by its group living and hunting habits. While less gregarious canids generally possess simple repertoires of visual signals, wolves have more varied signals that subtly inter grade in intensity. When neutral, the legs are not stiffened, the tail hangs down loosely, the face is smooth, the lips untensed, and the ears point in no particular direction. Postural communication in wolves consists of a variety of facial expressions, tail positions and piloerection. Aggressive, or self-assertive wolves are characterized by their slow and deliberate movements, high body posture and raised hackles, while submissive ones carry their bodies low, sleeken their fur and lower their ears and tail. When a breeding male encounters a subordinate family member, it may stare at it, standing erect and still with the tails horizontal to its spine. Two forms of submissive behavior are recognized: passive and active. Passive submission usually occurs as a reaction to the approach of a dominant animal, and consists of the submissive wolf lying partly on its back and allowing the dominant wolf to sniff its anogenital area. Active submission occurs often as a form of greeting, and involves the submissive wolf approaching another in a low posture, and licking the other wolf's face. When wolves are together, they commonly indulge in behaviors such as nose pushing, jaw wrestling, cheek rubbing and facial licking. The mouthing of each other's muzzles is a friendly gesture, while clamping on the muzzle with bared teeth is a dominance display. Similar to humans, gray wolves have facial color patterns in which the gaze direction can be easily identified, although this is often not the case in other canid species. In 2014, a study compared the facial color pattern across 25 canid species. The results suggested that the facial color pattern of canid species is related to their gaze communication, and that especially gray wolves use the gaze signal in conspecific communication. Viral diseases carried by wolves include rabies, canine distemper, canine parvovirus, infectious canine hepatitis, papillomatosis, canine coronavirus, and foot and mouth disease. Wolves are a major host for rabies in Russia, Iran, Afghanistan, Iraq and India. In wolves, the incubation period is 8–21 days, and results in the host becoming agitated, deserting its pack, and travelling up to 80 kilometres (50 mi) a day, thus increasing the risk of infecting other wolves. Infected wolves do not show any fear of humans, with most documented wolf attacks on people being attributed to rabid animals. Although canine distemper is lethal in dogs, it has not been recorded to kill wolves, except in Canada and Alaska. The canine parvovirus, which causes death by dehydration, electrolyte imbalance, and endotoxic shock or sepsis, is largely survivable in wolves, but can be lethal to pups. Wolves may catch infectious canine hepatitis from dogs, though there are no records of wolves dying from it. Papillomatosis has been recorded only once in wolves, and likely doesn't cause serious illness or death, though it may alter feeding behaviors. The canine coronavirus has been recorded in Alaskan wolves, with infections being most prevalent in winter months. Bacterial diseases carried by wolves include brucellosis, lyme disease, leptospirosis, tularemia, bovine tuberculosis, listeriosis and anthrax. Wolves can catch Brucella suis from wild and domestic reindeer. While adult wolves tend not to show any clinical signs, it can severely weaken the pups of infected females. Although lyme disease can debilitate individual wolves, it does not appear to have any significant effect on wolf populations. Leptospirosis can be contracted through contact with infected prey or urine, and can cause fever, anorexia, vomiting, anemia, hematuria, icterus, and death. Wolves living near farms are more vulnerable to the disease than those living in the wilderness, probably because of prolonged contact with infected domestic animal waste. Wolves may catch tularemia from lagomorph prey, though its effect on wolves is unknown. Although bovine tuberculosis is not considered a major threat to wolves, it has been recorded to have once killed two wolf pups in Canada. Parasitic infections Wolves carry ectoparasites and endoparasites, with wolves in the former Soviet Union having been recorded to carry at least 50 species. Most of these parasites infect wolves without adverse effects, though the effects may become more serious in sick or malnourished specimens. Parasitic infection in wolves is of particular concern to people, as wolves can spread them to dogs, which in turn can carry the parasites to humans. In areas where wolves inhabit pastoral areas, the parasites can be spread to livestock. Wolves are often infested with a variety of arthropod exoparasites, including fleas, ticks, lice, and mites. The most harmful to wolves, particularly pups, is Sarcoptes scabiei (or mange mite), though they rarely develop full blown mange, unlike foxes. Lice, such as Trichodectes canis, may cause sickness in wolves, but rarely death. Ticks of the genus Ixodes can infect wolves with Lyme disease and Rocky Mountain spotted fever. The tick Dermacentor pictus also infests wolves. Other ectoparasites include biting lice, sucking lice and the fleas Pulex irritans and Ctenocephalides canis. Endoparasites known to infect wolves include protozoans and helminths (flukes, tapeworms, roundworms and thorny-headed worms). Of 30,000 protozoan species, only a few have been recorded to infect wolves: Isospora, Toxoplasma, Sarcocystis, Babesia, and Giardia. Wolves may carry Neospora caninum, which is of particular concern to farmers, as the disease can be spread to livestock, with infected animals being 3–13 times more likely to miscarry than those not infected. Among flukes, the most common in North American wolves is Alaria, which infects small rodents and amphibians that are eaten by wolves. Upon reaching maturity, Alaria migrates to the wolf's intestine, but harms it little. Metorchis conjunctus, which enters wolves through eating fish, infects the wolf's liver or gall bladder, causing liver disease, inflammation of the pancreas, and emaciation. Most other fluke species reside in the wolf's intestine, though Paragonimus westermani lives in the lungs. Tapeworms are commonly found in wolves, as their primary hosts are ungulates, small mammals, and fish, which wolves feed upon. Tapeworms generally cause little harm in wolves, though this depends on the number and size of the parasites, and the sensitivity of the host. Symptoms often include constipation, toxic and allergic reactions, irritation of the intestinal mucosa, and malnutrition. Infections by the tapeworm Echinococcus granulosus in ungulate populations tend to increase in areas with high wolf densities, as wolves can shed Echinoccocus eggs in their feces onto grazing areas. Wolves can carry over 30 roundworm species, though most roundworm infections appear benign, depending on the number of worms and the age of the host. Ancylostoma caninum attaches itself on the intestinal wall to feed on the host's blood, and can cause hyperchromic anemia, emaciation, diarrhea, and possibly death. Toxocara canis, a hookworm known to infect wolf pups in utero, can cause intestinal irritation, bloating, vomiting, and diarrhea. Wolves may catch Dioctophyma renale from minks, which infects the kidneys, and can grow to lengths of 100 cm. D. renale causes the complete destruction of the kidney's functional tissue, and can be fatal if both kidneys are infected. Wolves can tolerate low levels of Dirofilaria immitis for many years without showing any ill effects, though high levels can kill wolves through cardiac enlargement and congestive hepatopathy. Wolves probably become infected with Trichinella spiralis by eating infected ungulates. Although T. spiralis isn't known to produce clinical signs in wolves, it can cause emaciation, salivation, and crippling muscle pains in dogs. Thorny-headed worms rarely infect wolves, though three species have been identified in Russian wolves: Nicolla skrjabini, Macrocantorhynchus catulinus, and Moniliformis moniliformis. Wolly [